1. Field of the Invention
This invention relates in general to well drilling apparatus and more particularly to devices for regulating the movement of a drill string or pipe utilized in well drilling.
2. Description of the Prior Art
In the past, most oil drilling apparatus have utilized a draw works consisting of a powered rotating drum for raising and lowering the drill string by means of a drilling cable. The drilling cable is carried on the powered rotating drum of the draw works and is received through sheaves located in the crown and traveling block. The traveling block is connected to a drill string pipe such that rotation of the draw works drum raises and lowers the drill string pipe.
In most well drilling apparatus the draw works is operated by means of a clutch which is connected to and actuated by pressurized air from an air supply. An air valve regulates the supply of air from the air supply to the draw works clutch to engage the draw works. The air valve is generally located on a driller's console so that a driller operator can manually engage the draw works by means of this valve.
Most well drilling apparatus also include a blowout prevention device which locks or freezes the drill string pipe in position. This prevents the pipe from being lifted out of the well due to pressure changes within the well. The blow out prevention device also usually cuts off the supply of mud which is circulated into the well during the drilling process. The blow out preventer includes hydraulically actuated rams which engage the drill string pipe when hydraulic pressure is supplied to the blow out preventer. Hydraulic pressure is supplied to the blow out preventer from a source of hydraulic fluid generally known as an accumulator. The accumulator also supplies hydraulic fluid for various hydraulically operated devices around the drilling apparatus. A particular valve on the accumulator supplies hydraulic pressure to the blow out preventer and engages the rams with the drill string pipe, locking the pipe against movement.
In the past, a particular problem with well drilling apparatus has been that the blow out prevention device has often been engaged when the draw works has been inadvertently or absent-mindedly operated. When this happens, the drill string pipe will be damaged and often the pipe is severed. Usually various other equipment is destroyed in the effort to move the locked drill pipe. If severed, the pipe often falls into the hole and is lost either before or after the blow out preventer is disengaged.
In most well drilling apparatus the accumulator and its valves, and the driller's console and the draw works valve are not located in the same position. This prevents immediate mechanical connection between the blow out prevention accumulator valve and the draw works control valve. Moreover, a mechanical connection would interfere with the regular operation of the draw works.